Various specific embodiments of interferometric measuring devices for the three-dimensional measuring of shapes on objects to be measured are described, for example, in connection with classic interferometry (see, e.g., A. Donges, R. Noll in “Lasermesstechnik” [Laser Metrology], Hüthig Publishers 1993), white-light interferometry, where light sources of short coherence length are used (e.g., light-emitting diode, superluminescent diode) (compare P. de Groot, L. Deck, “Surface Profiling by Analysis of White-Light Interferograms in the Spatial Frequency Domain” J. Mod. Opt., vol. 42, no. 2, 389-401, 1995; Th. Dresel, G. Häusler, H. Venzke; “Three-Dimensional Sensing of Rough surfaces by Coherence Radar”, Appl. Opt., vol. 31, no. 7, 919-925, 1992; German Patent Application Nos. DE 199 48 813.4 and DE 100 15 878.1) and heterodyne interferometry (see, e.g., DE 197 21 842 C2; H. J. Tiziani, “Optical Methods for Precision Measurements”, Optical and Quantum Electronics, vol. 21, 253-282, 1989; K. Creath, “Temporal Phase Measurement Method” in d. W. Robinson, T. G. Reid: “Interferogram Analysis”, IOP Publishing Bristol 1993; R. Onodera, Y. Ishii, “Two-Wavelength Interferometry That Uses a Fourier Transform Method”, Appl. Opt., vol. 37, no. 34, 7988-7994, 1998).
White-light interferometry established itself as a method of measurement particularly for the three-dimensional measuring of shapes. The setup is typically implemented using a Michelson interferometer. The object is imaged on an image pickup, for example of a CCD camera, via an objective located in an object light path and is superimposed by a flat reference wave. The depth scanning (in the z-direction) may be performed as a scan of a reference mirror located in the reference light path or of the object. When scanning the object, the image plane of the objective and the reference plane are in the same plane. The object is moved only in the depth axis relative to the reference plane. When scanning the reference mirror, only the reference mirror is moved.
The object remains immobile with respect to the objective. In this instance, the depth measurement range is limited by the objective's depth of field. With this measuring method it is possible advantageously to measure industrial surfaces at a depth resolution of a few nm (1-10 nm).
An advantageous further development of a white-light interferometer is described in German Patent Application No. DE 101 15 524 A1, wherein an optical setup for producing a flat intermediate image is situated in the measuring light path, for example an endoscope optics. The depth scan may be implemented as a scan of the reference or as an intermediate image scan. A white-light interferometer including an intermediate image of the object or an endoscope is also described in German Patent Application No. DE 100 47 495 A1. These white-light interferometers also achieve a depth resolution of industrial surfaces of a few nm, while additionally allowing for measurements in narrow and deep bore holes.
In a further development of an optical 3-D measuring device described in German Patent Application No. DE 101 31 778 A1, likewise a white-light interferometer for example, an objective optics is situated on the object light path, which also makes it possible to measure curved surface regions or circumferential radial-symmetric surface regions, for example valve seats, a depth resolution of a few nm being achieved as well and measurement also being possible in narrow and deep bore holes.
German Patent Application No. DE 101 62 180 A1 describes arranging an electrically controllable filter in the measuring arm and/or reference arm of an interferometric measuring device in order to adjust the intensities of the reference beam and the measuring beam to each other.
In the measurement of real industrial surfaces using interferometric measuring devices of the kind mentioned, precise, reliable measurements, however, are frequently hampered by the given surface properties, particularly when special optics are used in order to conduct measurements in the case of special surface shapes.